1. Field of the Invention
The present invention generally relates to electro-optical systems, such as bar code symbol readers, and more particularly to a compact scan module for use in applications requiring at least two different laser beam characteristics.
2. Description of the Related Art
One-dimensional bar code symbols arc formed from bars typically rectangular in shape with a variety of possible widths and spaced apart by spaces of various widths. The specific arrangement of the bars and spaces defines the characters represented by the symbol according to a set of rules and definitions specified by the code or xe2x80x9csymbologyxe2x80x9d used. The relative size of the bars and spaces is determined by the type of coding used as is the actual size of the bars and spaces. The number of characters (represented by the bar code symbol) per unit length is referred to as the density of the symbol. To encode the desired sequence of the characters, a collection of bar and space arrangements are concatenated together to form the complete bar code symbol, with each character of the message being represented by its own corresponding group of bars and spaces. In some symbologies, a unique xe2x80x9cstartxe2x80x9d and xe2x80x9cstopxe2x80x9d character is used to indicate when the bar code begins and ends. A number of different bar code symbologies is in widespread use including UPC/EAN, Code 39, Code 128, Codabar, and Interleaved 2 of 5.
In order to increase the amount of data that can be represented or stored on a given amount of surface area, several more compact bar code symbologies have been developed. One of these code standards, Code 49, exemplifies a xe2x80x9ctwo-dimensionalxe2x80x9d symbol by reducing the vertical height of a one-dimensional symbol, and then stacking distinct rows of such one-dimensional symbols, so that information is encoded both vertically as well as horizontally. That is, in Code 49, there are several rows of bar and space patterns, instead of only one row as in a xe2x80x9cone-dimensionalxe2x80x9d symbol. The structure of Code 49 is described in U.S. Pat. No. 4,794,239. Another two-dimensional symbology, known as xe2x80x9cPDF417xe2x80x9d, is described in U.S. Pat. No. 5,304,786.
Still other symbologies have been developed in which the symbol is comprised not of stacked rows, but of a matrix array made up of hexagonal, square, polygonal and/or other geometric shapes, lines, or dots. Such symbols are described in, for example, U.S. Pat. Nos. 5,276,315 and 4,794,239. Such matrix code symbologies may include Vericode, Datacode, and MAXICODE.
Various optical scanning systems and readers have been developed heretofore for reading indicia such as bar code symbols appearing on a label or on the surface ol an article. The readers function by electro-optically transforming the spatial pattern represented by the graphic indicia into a time-varying electrical signal, which is in turn decoded into data which represent the information or characters encoded in the indicia that are intended to be descriptive of the article or some characteristic thereof. Such data is typically represented in digital form and utilized as an input to a data processing system for applications in point-of-sale processing, inventory control distribution, transportation and logistics, and the like.
One particularly advantageous type of reader is an optical scanner which scans a beam of light, such as a laser beam, across the symbols. Laser scanner systems and components have generally been designed to read indicia having parts of different light reflectivity, i.e., bar code symbols, particularly of the Universal Product Code (UPC) type, at a certain working range or reading distance from a hand-held or stationary scanner to the symbol or target.
In the laser beam scanning systems known in the art, a laser light beam from a light source is directed by a lens or other optical components along a light path toward a target that includes a bar code symbol on a target surface. The moving-beam scanner operates by repetitively scanning the light beam in a scan line or a series of scan lines across the symbol by means of motion of a scanning component, such as the light source itself or a mirror disposed in the path of the light beam. The scanning component may either sweep a beam spot across the symbol and trace the scan line or scan lines across the symbol, or scan the field of view of a sensor of the scanner, or do both. The laser beam may be moved by optical or opto-mechanical means to produce a scanning light beam. Such action may be performed by either deflecting the beam (such as by a moving optical element, such as a mirror) or moving the light source itself. U.S. Pat. No. 5,486,944 describes a scan module in which a mirror is mounted on a flex element for reciprocal oscillation by electromagnetic actuation. U.S. Pat. No. 5,144,120 to Krichever, et al. describes laser, optical and sensor components mounted on a drive for repetitive reciprocating motion either about an axis or in a plane to effect scanning of the laser beam.
Another type of bar code scanner employs electronic means for causing the light beam to be deflected and thereby scan the bar code symbol, rather than using a mechanical motion to move or deflect the beam. For example, a linear array of closely spaced light sources activated one at a time in a regular sequence may be transmitted to the bar code symbol to simulate a scanned beam from a single source. Instead of a single linear array of light sources, a multiple-line array of individual lasers may also be employed, thereby producing multiple scan lines. Such a bar code reader is disclosed in U.S. Pat. No. 5,258,605 to Metlitsky, ct al. The use of multiple discrete lasers is also described in U.S. Pat. No. 5,717,221.
Bar code reading systems also include a sensor or photodetector which detects light reflected or scattered from the symbol. The photodetector or sensor is positioned in the scanner in an optical path so that it has a field of view which ensures the capture of a portion of the light which is reflected or scattered off the symbol, detected, and converted into an electrical signal.
In retroreflective light collection, a single optical component, e.g., a reciprocally oscillatory mirror, such as described by Krichever, et al. in U.S. Pat. No. 4,816,661 or by Shepard, et al. in U.S. Pat. No. 4,409,470, both herein incorporated by reference, and U.S. Pat. No. 6,114,712, scans the beam across a target surface and directs the collected light to a detector. The mirror surface usually is relatively large to receive as much incoming light as is possible. Only a small detector is required since the mirror can focus the light onto a small detector surface, which increases signal-to-noise ratio.
A variety of mirror and motor configurations can be used to move the beam in a desired scanning pattern. For example, U.S. Pat. No. 4,251,798 discloses a rotating polygon having a planar mirror at each side, each mirror tracing a scan line across the symbol. U.S. Pat. Nos. 4,387,297 and 4,409,470 both employ a planar mirror which is repetitively and reciprocally driven in alternate circumferential directions about a drive shaft on which the mirror is mounted. U.S. Pat. No. 4,816,660 discloses a multi-mirror construction composed of a generally concave mirror portion and a generally planar mirror portion. The multi-mirror construction is repetitively reciprocally driven in alternate circumferential directions about a drive shaft on which the multimirror construction is mounted. U.S. Pat. No. 6,247,647 describes an arrangement for providing either a multiple line, or a single line, scan pattern by means of a controller. All of the above-mentioned U.S. patents are incorporated herein by reference.
In electro-optical scanners of the type discussed above, the implementation of the laser source, the optics, the mirror structure, the drive to oscillate the mirror structure, the photodetector, and the associated signal processing and decoding circuitry as individual components all add size and weight to the scanner. In applications involving protracted use, a large, heavy scanner can produce user fatigue. When use of the scanner produces fatigue or is in some other way inconvenient, the user is reluctant to operate the scanner. Any reluctance to consistently use the scanner defeats the data gathering purposes for which such bar code systems are intended. Thus, a need exists for a compact module to fit into small compact devices, such as electronic notebooks, portable digital assistants, pagers, cell phones, and other pocket appliances, which can serve multiple scanning applications.
Thus, an ongoing objective of bar code reader development is to miniaturize the reader as much as possible, and a need still exists to further reduce the size and weight of the scan module or engine and to provide a particularly convenient to use scanner. The mass of the moving components should be as low as possible to minimize the power required to produce the scanning movement, thereby saving battery power.
It is further desirable to modularize the scan engine so that a single module can be used in a variety of different scanning applications, such as a near field or far field reader, or reading one-dimensional or two-dimensional symbols with a single or multiple scan line pattern. A need exists to develop a particularly compact, lightweight scan module for different applications.
Accordingly, it is an object of the present invention to provide a scan module with selectable scan mirrors having different optical properties for use in a bar code reader.
A related object is to develop an electro-optical, compact scan module which enables the laser beam to be optically modified and customized for a particular application.
In keeping with these objects and others which will become apparent hereinafter, one feature of this invention resides, briefly stated, in an arrangement for scanning indicia in a system for electro-optically reading the indicia. The arrangement includes a support, a hub mounted on the support for turning movement about an axis, a plurality of optical elements mounted on the hub for joint movement therewith, and a drive for moving the elements. The hub, the elements, the drive and the support together constitute a compact scan module or engine for ready replacement in the system.
The elements are preferably scan mirrors having different optical characteristics. For example, one mirror may have a flat surface, and another mirror may have a convex surface. A laser beam having a generally circular cross-section will reflect off a flat mirror with the same circular cross-section, but will reflect off a convex mirror with an elliptical cross-section. The circular cross-section is better for reading two-dimensional symbols, whereas the elliptical cross-section is better for reading one-dimensional symbols. The mirrors direct the beam incident thereon as an optically modified beam along an optical path toward the indicia to be read.
The drive selectively positions one of the mirrors at a reference position in the optical path and, once so positioned, the drive oscillates the positioned mirror about the axis. Preferably, the reference position is a central position, and the oscillation is back-and-forth in opposite directions relative to the central position of a respective scan line on and across the indicia.
In the preferred embodiment, the drive includes a permanent magnet on the hub, a first electromagnetic coil which, when energized, generates a first magnetic field that interacts with the permanent field of the magnet to turn the magnet and the hub, and a second electromagnetic coil which, when energized, generates a second magnetic field that interacts with the permanent field to turn the magnet and the hub. The coils are angularly spaced apart about the axis and are selectively energized. Each coil is energized by a periodic, alternating drive signal so that the hub oscillates.
The drive also includes a first pole piece for the first coil, and a second pole piece for the second coil. Each pole piece is constituted of a ferromagnetic material and, by interaction with the magnet, defines a respective reference position or starting point relative to which the hub oscillates.
By selecting one mirror, the light incident thereon is swept across the indicia with a certain optical characteristic, for example, a beam spot of a certain cross-section as described above. By selecting another mirror, a beam spot of a different cross-section is swept across the indicia. Selection of the beam spot can be performed manually or automatically. The different properties of the beam spot can be employed to read one-dimensional or two-dimensional symbols, or to preferentially read close-in or far-out symbols, or to read symbols of different densities.
The scan module can be used by itself in a reader to obtain scanning in one direction across a symbol, either across the length or width of the symbol. The scan module can be used with another scan module to obtain scanning in mutually orthogonal directions across the symbol. It is currently preferred when the scan module of this invention is used to sweep a laser beam over relatively small arc lengths on the order of xc2x13xc2x0 degrees mechanical.